1. Field of the Invention
This invention relates to a photographic emulsion, in particular, to a silver halide photographic emulsion containing a novel copolymer.
2. Description of the Prior Art
Gelatin is widely used as a protective colloid as well as halogen acceptor and retainer in the manufacture of silver halide photographic emulsions. In addition, gelatin has an excellent gel-forming action. On the other hand, however, gelatin which is a natural substance, has disadvantages in that an emulsion of uniform quality cannot be obtained using gelatin due to a small amount of impurities contained in the gelatin and due to decay of the gelatin during storage thereof. In addition, gelatin tends to be hydrolyzed during the manufacture of silver halide emulsions and the resulting hydrolyzed product affects the properties of the emulsions formed. Therefore, it is difficult to manufacture photographic materials of uniform quality using gelatin. In the manufacture of silver halide photographic materials, some attempts have already been effected to try to substitute a part or all of the gelatin with other synthetic products (for example as disclosed in Japanese Pat. No. 164,435; Japanese Patent Publication No. 7561/68; British Pat. No. 788,343; U.S. Pat. No. 2,811,494, etc.). In the prior art, however, it has been extremely difficult to manufacture synthetic products which have excellent gelation effects and which have the protective colloid qualities equal to gelatin. In addition, it also is difficult to manufacture synthetic products which are stable to pH variations during manufacture of silver halide emulsions. A large number of polymers are used as additives for gelatin, but they are necessarily limited to those which are compatible with gelatin. However, when a large amount of such a synthetic product is used, a hazed mixture is manufactured, or a reticulated film is formed after drying of the emulsion. In addition, when a mixture of a synthetic product and gelatin is used, the polymer tends to separate from the emulsion formed with variations in the pH thereof, or a hazed film is formed. On these grounds, the manufacture of synthetic products that are stable to pH variations, even after a part or all of the gelatin is substituted by such product, has been earnestly desired. In addition, it also is desired that these synthetic products be used in the manufacture of photographic films and papers and in silver halide emulsion layers, filter layers, intermediate layers, etc.